At present fluid bed type granulator devices are known, which are generally used for the treatment of powdered materials and which basically comprise cylindrical containers with sealed walls, delimiting a chamber for treatment of the materials, a plurality of filtering means with solid walls, projecting into the treatment chamber, means for conveying an operating fluid flow, through the chamber, and cleaning means designed to remove dust from and wash the permanent filters.
The methods for removing dust from and washing the filtering means, designed to restore filtering means which have become clogged or less efficient to their former operating state, or to prepare the device for treating a material different to that treated in a previous processing cycle, have a critical role in many technologies for powders used, for example, in some chemical or pharmaceutical products.
Said dust removal methods must be carried out suitably in order to prevent the operating fluids entering the device from contaminating the powdered material and/or the operating fluids exiting the device from contaminating the environment, and/or to prevent the maintenance operations for the filters and the other operating parts of the device from being hazardous to the health of the personnel who perform them and the surrounding environment.
A granulator device of the type described above is known for example from U.S. Pat. No. 5,868,807, in which the filtering means consist of substantially tubular elements with rigid, filtering cylindrical outer walls, formed by a number of layers of metal mesh placed on top of one another and made into a single body by means of a sintering process.
According to the method described in said United States patent, the removal of dust from and washing of the filtering means are therefore achieved respectively by blowing compressed air, against the flow, through the wall of each filter, said air blown in by stationary nozzles covering the entire filtering surface of each of the filters, and by washing the outer surface of the filters by supplying a flow of water which is diffused by special nozzles, also stably supported by the outer walls of the container which circumscribes the product treatment chamber.
The device structured in this way allows the achievement of a degree of cleaning of the filtering means which is satisfactory for most applications in particular during the treatment of powdered materials for pharmaceutical use, but is very complex from the construction viewpoint, is very expensive and it is particularly difficult to check its operation.
One solution to such disadvantages is known from International Patent application PCT WO2005/014157 filed by the Applicant. It is a method for cleaning filters located in a granulator device, using an arm which rotates about each sintered metal mesh filter and supports diffuser nozzles designed to diffuse a service fluid (air and/or washing liquid) on the outer walls of the filters, internally and/or externally, so as to progressively cover the length of the walls and remove any impurities from them.
Said cleaning method proved effective, but only where the quantities of impurities were not significant. If large quantities of impurities build up at predetermined points of the filters, the service fluid cannot always perfectly dissolve and disperse said build ups.